Breathlessness dry cough chest pain expectoration what are the investi

Breathlessness dry cough chest pain expectoration what are the investigations to be advised and why

Reading File

Finding Sources

Searching PubMed

dyspnea AND diagnosis

Searching the Web

NICE breathlessness chest pain cough assessment investigations ECG chest x ray oxygen saturation guidelines

Finding Sources

Breathlessness with chest pain and cough, whether dry or with sputum, needs prompt clinical assessment because causes range from respiratory infection or asthma/COPD to heart failure, pulmonary embolism, pneumothorax, or acute coronary syndrome.

Seek emergency care now if symptoms are sudden/severe, chest pressure or pain spreading to arm/jaw/back, blue lips, fainting, confusion, coughing blood, oxygen saturation below 92% if measured, or fever with marked deterioration.

Initial investigations

Investigation	Why it is advised
Vital signs and pulse oximetry: respiratory rate, pulse, BP, temperature, oxygen saturation	Establishes severity, detects hypoxaemia, fever, shock, or tachycardia, and helps decide whether urgent admission and oxygen are needed. NICE recommends an ABC assessment and measurement of oxygen saturation in breathlessness.
12-lead ECG	Chest pain and breathlessness can be due to myocardial ischaemia/infarction, arrhythmia, right-heart strain from pulmonary embolism, or heart failure.
Chest X-ray	Looks for pneumonia, pleural effusion, pulmonary oedema/heart failure, pneumothorax, lung mass, or other lung abnormalities. It is a key first-line test for unexplained dyspnoea.
Full blood count (FBC)	High white-cell count may support infection; low haemoglobin may cause or worsen breathlessness; eosinophilia may support an allergic/eosinophilic process.
CRP, and sometimes procalcitonin	Helps assess inflammation/infection and supports clinical assessment for pneumonia, though these tests alone cannot diagnose bacterial infection.
Urea, electrolytes, creatinine, liver function, glucose	Identifies metabolic contributors and organ dysfunction; provides baseline before contrast CT or certain medicines.
Troponin, with repeat testing if acute cardiac pain is possible	Detects myocardial injury/acute coronary syndrome. This is urgent when pain is pressure-like, exertional, associated with sweating/nausea, or there are cardiac risk factors.
Arterial blood gas (ABG) or venous blood gas, as appropriate	If hypoxic, severely breathless, drowsy, or known COPD: assesses oxygen, carbon dioxide retention, and acid-base status.
Sputum microscopy, Gram stain and culture	If there is purulent sputum, fever, recurrent infection, severe pneumonia, treatment failure, bronchiectasis, or hospital admission. It can identify a bacterial pathogen and antibiotic susceptibility. A good-quality early sample is important.
Viral testing: COVID-19/influenza/RSV, according to local prevalence and setting	Identifies transmissible viral respiratory infections and may affect isolation and treatment decisions.
Blood cultures	Not routine for mild illness, but advised before antibiotics in severe pneumonia, sepsis, ICU admission, or suspected bacteraemia.
BNP or NT-proBNP	If heart failure is suspected, especially with orthopnoea, leg swelling, raised JVP, crackles, or pulmonary oedema on X-ray.
Echocardiography	If ECG/BNP/examination suggests heart failure, valvular disease, pulmonary hypertension, or pericardial disease.
D-dimer	Only when pulmonary embolism is clinically plausible and pre-test probability is low/intermediate. A negative result can help exclude PE in appropriate patients.
CT pulmonary angiography (CTPA) or V/Q scan	If pulmonary embolism is likely or D-dimer is positive. Sudden breathlessness, pleuritic chest pain, tachycardia, haemoptysis, recent surgery/immobility, pregnancy/postpartum state, prior DVT/PE, or unilateral leg swelling raise concern.
Leg-vein Doppler ultrasound	Looks for DVT when PE is suspected, especially with unilateral leg pain or swelling.
Spirometry with bronchodilator reversibility	Performed when the acute episode has settled if asthma or COPD is suspected. It confirms airflow obstruction and assesses reversibility. It should not delay emergency assessment in acute distress.
CT chest / HRCT chest	Not first-line routinely. Consider after X-ray or specialist review for suspected interstitial lung disease, bronchiectasis, malignancy, complicated infection, or unexplained persistent symptoms.

A practical first-line set

For a person currently presenting with these symptoms, a reasonable initial panel is:

Clinical examination, vital signs and oxygen saturation
ECG
Chest X-ray
FBC, CRP, renal/electrolyte profile, glucose
Troponin if the chest pain could be cardiac
ABG/VBG if hypoxic or significantly unwell
Sputum culture if sputum is purulent, persistent, or infection is suspected
D-dimer followed by CTPA only when PE risk assessment indicates it
BNP and echocardiography if heart failure is suspected

Testing should be guided by onset, pain character, fever, smoking/exposure history, age, cardiac risks, pregnancy status, immobility/surgery, leg symptoms, and examination findings. The NICE breathlessness assessment guidance supports early assessment of ABCs, oxygen saturation, associated chest pain/cough, and cardiorespiratory examination; NICE cough guidance lists chest X-ray, FBC, and spirometry among common initial investigations for persistent cough.

How to read ABG report

Reading File

Finding Sources

Searching PubMed

arterial blood gas interpretation acid base

Searching the Web

arterial blood gas interpretation pH PaCO2 HCO3 compensation reference ranges clinical guideline

How to read an ABG report: a stepwise method

An arterial blood gas (ABG) evaluates acid-base status, ventilation, and oxygenation. Interpret it in this order:

1. Check pH: acidaemia or alkalaemia?

pH	Interpretation
7.35-7.45	Normal
< 7.35	Acidaemia
> 7.45	Alkalaemia

A pH within the normal range does not rule out illness. It may mean a fully compensated disorder or a mixed acid-base disorder.

2. Identify the primary process using PaCO₂ and HCO₃⁻

Usual reference ranges:

Value	Typical range	Main role
PaCO₂	35-45 mmHg	Respiratory component
HCO₃⁻	22-26 mmol/L	Metabolic/renal component
Base excess (BE)	-2 to +2 mmol/L	Metabolic component
PaO₂	roughly 80-100 mmHg on room air in a healthy young adult	Oxygenation
Oxygen saturation	about 95-100%	Oxygenation

Rule:

CO₂ acts opposite to pH
- High PaCO₂ causes acidosis
- Low PaCO₂ causes alkalosis
Bicarbonate acts in the same direction as pH
- Low HCO₃⁻ causes acidosis
- High HCO₃⁻ causes alkalosis

pH / primary change	Diagnosis
Low pH + high PaCO₂	Respiratory acidosis
Low pH + low HCO₃⁻	Metabolic acidosis
High pH + low PaCO₂	Respiratory alkalosis
High pH + high HCO₃⁻	Metabolic alkalosis

3. Assess whether compensation is appropriate

Compensation means the other system responds to reduce, but not completely correct, the pH abnormality. Compensation should not overshoot and create alkalosis or acidosis on its own.

A. Metabolic acidosis

For low HCO₃⁻, calculate expected PaCO₂ using Winter's formula:

[ \text{Expected PaCO₂} = (1.5 \times \text{HCO₃⁻}) + 8 \pm 2 ]

Actual PaCO₂ within the range: appropriate respiratory compensation
Actual PaCO₂ higher than expected: additional respiratory acidosis
Actual PaCO₂ lower than expected: additional respiratory alkalosis

Example: pH 7.20, HCO₃⁻ 12, PaCO₂ 26.

Expected PaCO₂ = (1.5 × 12) + 8 = 26 ± 2.
This is metabolic acidosis with appropriate respiratory compensation.

B. Metabolic alkalosis

Expected respiratory compensation:

[ \text{Expected PaCO₂} = (0.7 \times \text{HCO₃⁻}) + 20 \pm 5 ]

If measured PaCO₂ is substantially outside this range, suspect an additional respiratory disorder.

C. Respiratory acidosis

For every PaCO₂ rise of 10 mmHg above 40:

Acute: HCO₃⁻ rises by about 1 mmol/L
Chronic: HCO₃⁻ rises by about 3.5-4 mmol/L

Examples:

pH 7.25, PaCO₂ 60, HCO₃⁻ 26: likely acute respiratory acidosis
pH near normal, PaCO₂ 60, HCO₃⁻ 32: likely chronic compensated respiratory acidosis, often seen in chronic CO₂ retainers such as some patients with COPD.

D. Respiratory alkalosis

For every PaCO₂ fall of 10 mmHg below 40:

Acute: HCO₃⁻ falls by about 2 mmol/L
Chronic: HCO₃⁻ falls by about 4-5 mmol/L

A useful detailed compensation table and Winter's formula are described in this clinical blood-gas guide.

4. If there is metabolic acidosis, calculate the anion gap

[ \text{Anion gap} = Na^+ - (Cl^- + HCO₃^-) ]

Typical normal anion gap is about 8-12 mmol/L, but always use your laboratory's reference range.

High-anion-gap metabolic acidosis

Think of:

Lactic acidosis: sepsis, shock, hypoxia
Ketoacidosis: diabetic, alcoholic, starvation
Renal failure
Toxins/drugs: salicylates, methanol, ethylene glycol

Normal-anion-gap metabolic acidosis

Think of:

Diarrhoea or intestinal bicarbonate loss
Renal tubular acidosis
Excess chloride-containing IV fluids

If albumin is low, the anion gap may look falsely normal. A commonly used correction is:

[ \text{Corrected AG} = \text{measured AG} + 2.5 \times (4 - \text{albumin in g/dL}) ]

5. Assess oxygenation separately

Review:

PaO₂
Oxygen saturation
FiO₂, meaning whether the patient is on room air or supplemental oxygen

A low PaO₂ indicates hypoxaemia. Its importance depends on age, altitude, and oxygen being administered. A PaO₂ that seems acceptable while the patient is receiving high-flow oxygen may still represent serious respiratory failure.

For a patient with breathlessness, high PaCO₂ suggests hypoventilation or ventilatory failure. Low PaCO₂ may result from hyperventilation due to hypoxaemia, pulmonary embolism, pneumonia, pain, anxiety, or sepsis.

Quick pattern-recognition table

ABG pattern	Interpretation	Typical examples
pH ↓, PaCO₂ ↑, HCO₃⁻ normal/slightly ↑	Acute respiratory acidosis	Opioid toxicity, acute severe COPD/asthma, neuromuscular weakness
pH near normal, PaCO₂ ↑, HCO₃⁻ ↑	Chronic respiratory acidosis with compensation	Chronic hypercapnic COPD, obesity hypoventilation
pH ↑, PaCO₂ ↓	Respiratory alkalosis	Pulmonary embolism, early sepsis, pain/anxiety, hypoxaemia
pH ↓, HCO₃⁻ ↓	Metabolic acidosis	DKA, lactic acidosis, renal failure, diarrhoea
pH ↑, HCO₃⁻ ↑	Metabolic alkalosis	Vomiting, nasogastric loss, diuretics

Worked examples

Example 1

pH: 7.28
PaCO₂: 60 mmHg
HCO₃⁻: 27 mmol/L

Interpretation: Acidaemia. PaCO₂ is high in the acidifying direction. Bicarbonate has risen only slightly.
Conclusion: Acute respiratory acidosis, possibly with minimal compensation.

Example 2

pH: 7.18
PaCO₂: 25 mmHg
HCO₃⁻: 9 mmol/L

Interpretation: Acidaemia with low bicarbonate.
Winter's expected PaCO₂ = (1.5 × 9) + 8 = 21.5 ± 2. Actual PaCO₂ is 25, higher than expected.
Conclusion: High-severity metabolic acidosis with concurrent respiratory acidosis. This needs urgent clinical assessment.

Example 3

pH: 7.49
PaCO₂: 29 mmHg
HCO₃⁻: 22 mmol/L

Interpretation: Alkalaemia with low PaCO₂.
Conclusion: Acute respiratory alkalosis.

One-line ABG reporting format

Use this structure:

“This ABG shows [acidaemia/alkalaemia], due primarily to [metabolic/respiratory] [acidosis/alkalosis], with [appropriate/inadequate] compensation. There is [hypoxaemia/no hypoxaemia] on [room air/oxygen], and the anion gap is [normal/high] if metabolic acidosis is present.”

Example:

“The ABG shows acidaemia due to metabolic acidosis, with appropriate respiratory compensation by Winter's formula. There is significant hypoxaemia on room air.”

ABGs must be interpreted alongside symptoms, respiratory rate, oxygen delivery, serum electrolytes, lactate, ketones, renal function, ECG, and chest imaging. A pH below 7.20, PaCO₂ rising with drowsiness, or low oxygen saturation is potentially urgent.

This is a shared conversation. Sign in to Orris to start your own chat.